Bomb sight and pilot director



y 1933. M. F. BATES BOMB SIGHT AND PILOT DIRECTOR Original Filed-July 18, 1931 3 Sheets-Sheet l INVENTO MORTIMER July 25, 1933. M. F. BATES BOMB SIGHT AND PILOT DIRECTOR Original Filed July 18, 1931 3 Sheets-Sheet 2 ATTORNEY INVENTOR fiT/MER F BHTES July 25, 1933. M. F. BATES BOMB SIGHT AND PILOT DIRECTOR 3 Sheets-Sheet 3 I I I I I I I I l I I l I I I I I I I I I I I I I I I I l l I iii" INVENTOR ORTIMER F5 755 4 Patented July 25, 1933 UNITED STATES PATENT 7 OFFICE MORTIMER F. BATES, OF BROOKLYN, NEW YORK, ASSIGNOR TO SPERRY GYROSCOPE COMPANY, INC., OF BROOKLYN, NEW YORK, A CORPORATION OF NEW YORK BOMB SIGHT AND PILOT DIRECTOR Application filed my 18, 1931, Serial This invention relates to bomb sights for aircraft and particularly to that part of the mechanism which directs the course of the airplane: so that its ground track passes through the target or other objective in a straight line before and/or at the instant of bomb release. For the purpose of this description, the ground track may be defined as a projection of the path of the airplane on the ground. Said projection is usually not quite vertical, the amount of departure from the vertical being dependent on the drift angle due to a cross wind, that is, the angle the longitudinal axis of the airplane makes with the ground track when projected thereon.

On account of the high efliciency of antiaircraft gunfire, bombing airplanes are today forced to a high altitude on the order of 20,000 feet. At such altitudes an appreciable wind is nearly always present, the direction and velocity of which is unknown to the aviator. The ground track of the airplane, therefore, is not parallel to the longitudinal axis of the aircraft except when going up or down wind. One of the most important factors in securing the correct range angle is the ground speed of the' aircraft along the straight portion of the ground track through the target. Instruments are available for determining the ground speed accurately provided the airplane arrives at a straight portion of the ground track before reaching the range angle. One of the principal problems for successful bombing, therefore, is this aligning operation, that is, the maneuvering of the airplane in the face of the unknown Wind factor so as to set up. a correct drift angle that will align the straight portion of the ground track with the target. It is self evident that the quicker the airplane can be maneuvered into this position the better, and once it is in this position it is also self evident that it should be held in this position until after the release of the bomb. I prefer, therefore, to employ in connection with my bombsight aligning mechanism a connection between said mechanism and the steering means whereby the sighting and aligning operation of the bomber also 110 551554. Renewed m 25, 1932.

causes the correct turning of the craft until the ground track becomes a straight line. Such turning may either be effected through a human agency, that is, through the operation of electrical signals to the human pilot, or automatically from the bomb sight through the operation of electrical impulses to an automatic pilot.

Another object of my invention is to improve on the system of steering an airplane from the sighting and aligning mechanism shown in prior Patent No. 1,783,769 dated December 2, 1930 and application No. 400,499, filed October 18, 1929. j

Another improvement effected by my invention lies in a method of automatically directing an aircraft toward its objective or destination by the shortest path, i. e., a straight ground track, regardless of side winds, by modifying or altering the heading of the craft from a position pointing directly at the objective through an angle substantially equal and opposite to the drift angle of the plane. Other objects of my invention Will be apparent as the description proceeds.

Referring to the drawings,

Fig. 1 is a diagrammatic development of my bombsight as applied to the control of the course of the airplane.

Fig. .2 is a detail of one of the prisms used in the optical system.

Fig. 3 is a diagrammatic view illustrating how the invention solves the problem of target approach.

Fig. 4 is a series of diagrams showing how the target appears through the sighting reticule in the various positions of aircraft and target illustrated in Fig. 3.

Fig. 5 is a sectional detail of the manual control handle of the sight.

Fig. 6 is a detail section of the middle poriion of said handle, taken at right angles to Fig. 7 is a diagram showing a modified form of my inventlon.

The optical system of my invention may assume different forms but I have illustrated a system similar to that shown and described in the aforesaid prior patent and application whereln the line of sight starting at the eyepiece 1 passes through a reticule 2 stabilized by being mounted on a gyro vertical 3, said gyroscope being universally mounted in the usual manner. After passing through the reticule with its cross hairs thereon, the line of sight is reflected substantially horizontally along the dotted line ab by means of roof prism 4 shown in detail in Fig. 2. The line of sight passes first through an objective lens 5 and then through a dove prism 6 which 1s mounted to rotate about the axis a b as by being mounted to turn with gear 7. The line of sight is then reflected downwardly by refleeting prism 8. Said prism 8 is mounted for rotation about its lateral axis CD so that by turning said prism on said axis any object on the ground may be followed as it is approached by the airplane if the airplane is flying directly toward the target and the object lies directly below and in the line ofv sight. In order that targets to one side of this line may be quickly sighted, the prlsm 8 is also mounted for tilting about the axis a-b, in other words, the fore and aft axis of the craft. For this purpose the prism may be mounted within the gear 9 which is connected through a one to two ratio of movement with respect to the dove prism 6 by means such as gearing 1011 so that the prism 6 turns through one half the angle of movement of the prism 8. The entire sighting device is mounted for rotation in azimuth. For this purpose there is shown a rotatable platform-12 which carries all the mechanism enclosed within the dotted lines in Fig. 1 except the stationary bottom gear 13 from which the platform is rotated.

The actual rotation of the platform is preferably accomplished through a variable speed drive 14 controllable from control handle 15. Said variable speed drive is shown as comprising a constantly driven motor 16 which rotates a cylinder 17. Beneath said cyllnder is shown a friction disc 18 and between said cylinder and disc is a ball drive 19 usually known as a two ball integrator. It will be quite apparent that when the balls heat the exact center of the disc, no rotation will be imparted to the disc while movement of the balls radially in one direction or the other will drive the disc in one direction or the other from the cylinder 17 and at a speed proportional to the distance of the balls from the centerof the disc. Disc 18 is shown as rotating the platform 12 by means of a pinion 20 on the shaft of the disc which meshes with a stationary internal gear 13. The balls are shown as positioned from the handle 15 by means of an arm 21 mounted on a hollow shaft 22 and operating between spring pressed centralizing bumpers 23 and 24. The arm 22 is preferably not permanently connected to the handle 15 but is detachably coupled thereto by means of a latch '25piy-\ oted within the handle. When the latch is in the osition shown in Fig. 1, rotation of the handle will turn the arm 21 rotating the pinion 22 and driving therefrom through suitable gearing connections 23' a pinion 24' which ositions the rack bar 25 connected to the two all integrator. Preferably the connections are such that disc 18 is stationar when the handle 15 is vertical, rotates the omb sight to the left when the handle is moved to the right, and rotates the bomb sight to the right when the handle is moved to the left.

Preferably I em loy the same handle 15 for laterally tilting tlEe reflector 8 for initially picking up the target. For this purpose there is shown a second arm 26 pivoted on the opposite side of the handle 15 and also detachably connected therewith through a latch which is preferably the opposite end 25' of the latch 25. Said arm likewise operates between spring-pressed centralizing bumpers 23-24" and has mounted on the hollow shaft 27 thereof a gear 28 driving a pinion 29. Said pinion is shown as driving a shaft 30 by means of drive 31. Shaft 30 operates the tilting mechanism for the reflector 8 preferably through a differential 31', the opposite side 32 of which is driven in accordance with a function of the drift angle in order to introduce the offset correction as hereinafter explained. The output of said differential drives the shaft 33 which is shown as turning the above described ear 7 through a pinion 34, gear 7 turning t e gear 9 through the above described two to one gear connection 1011.

In order that the aviator may follow the target after being picked up and synchronized therewith, I also provide a variable speed drive for turning the prism about the axis CD. For this purpose I have shown a constant speed motor 35 driving a disc 36 with a two ball integrator 37 between the disc and a driven cylinder 38. A hand crank 39 is provided for quickly positioning the line of sight on the target. The positioning of said two ball integrator to establish synchronism is preferably controlled from the same control handle 15-. For this purpose I have shown mounted on the control handle hand wheels 4040 which are journalled on top of the handle on a cross shaft 41 which drives through longitudinally extending shaft 43 and two pairs of bevel gears 44-45 an inner transverse shaft 43. Between the shaft 43 and the two ball integrator I preferably interpose a differential connection from the handle to prevent movement of the integrator 38 by rotation of the handle 15 about its axis. For this purpose gear '46 on shaft 43 forms one arm of a differential, the opposite arm 47 being turned from shaft 48 of the above deshaft 53. Said shaft in turn drives the pinion the two ball integrator by turning a gear 54:"

threaded on screw 54' similar to the drive from the motor 16. The cylinder 38, therefore, may be set to drive the reflector at its proper speed to keep the target in view.

In order to simplify the positioning of the integrator at the proper point, I prefer to put in an additional (orrective drive because otherwise if the operator has set his handle so that the integrator is traveling too slowly, he will have to move the handle far enough not only to cause the integrator to travel at the same speed as the target but also so as to make up for the distance that the target has been left behind. Therefore, when the sight catches up with the target it will be moving too fast and over-shoot. To avoid this I place an additional connection directly between the setting means 40, i. e., shaft 53,

and the screw 57 which turns the reflector. Preferably the ratio is such that the unit is moved along the screw 57 through a greater and preferably twice the distance the ball integrator is moved, so that a movement of wheel 40 will cause an immediate noticeable movement of the prism. For this purpose the shaft 53 is shown as turning one arm 58 of a differential, the opposite arm 59 being driven from the cylinder 38 and the screw shaft 57 being connected to the planetary arm. Screw 57 is shown as passing through a nut 60 adjustably mounted in a slot 61 in bell crank lever 62, the latter being pivoted at 63. The short arm of said lever is shown as pinned at 64 to a link 65 which is pinned at its opposite end to crank 66 on the shaft 67 of pinion 68 which drives through idlers 69 the rack bar 70. Rack bar 70 is shown as provided with a vertical shaft 71 having a connection with the reflector 8 such that movement of the rack longitudinally tilts the reflector 8 about the axis C-D, while at the same time the connection does not interfere with the lateral tilting of the reflector about axis ab. As shown, the shaft 71 engages a transverse trackway 72 in a carriage 73 so that the carriage moves with the rack longitudinally, but can tilt independently laterally with the reflector. The ratio is such (2: 1) that the reflected line of sight makes the same angle as member 62 makes with the vertical.

Since. the offset angle is a function of the drift angle I have shown mechanism actuated by the turning of the sight with respect to the airplane for introducing the offset angle thro pinion 105 mounted on the rotatable portion of the bomb sight meshes with a stationary internal gear13. Said pinion drives a worm 106 turning a worm wheel 107, the latter having an adjustable eccentric pin 108 mounted on a disc 109 secured to the shaft 110 of the worm wheel. Pin 108vwi1l, therefore, reciprocate the rack bar 111 inaccordance with the .on a cam roller 65.

ugh differential 32. For this purpose.

cosine of the drift angle, the pin also being adjustable by means of a thumb screw 112 to vary the throw thereof for any particular or average trail angle factor. Rack bar 111 is shown as turning the gear 32 through a pinion 113 and drive 114. The direction of this offset angle is tilted about axis ab of prism 8, to the right for right hand rotation of sight in azimuth and vice versa.

As stated in the preamble, I provide a means associated with the sighting or aligning means for quickly turning the airplane into the position in which the ground track to the target is a straight line. For this purpose during the initial aligning operation which consists in first aligning the fore and aft line of the craft with the target, illustrated diagrammatically in Fig. 3, as bringing the aircraft from position A to position B, it is necessary to cause a turn of the aircraft toward the target until theprism axis CD is relatively horizontal. I, therefore, provide a means for effecting such turning when the latch 25 is in engagement with the sector 26 and the handle 15 is tilted. This means may comprise pilot directing indicator 70, which may be driven by any suitable means 71 from the sleeve 27. When the handle 15 is vertical the indicator 70 indicates a straight course. when it is tipped to the right the indicator 7 0 shows that the airplane should be turned to the right and vice versa.

As soon as the airplane has reached position B, the airplane and bomb sight are then in a position to begin the final alignin process. In this process I prefer. to followthe target by turning the entire bomb sight around its vertical axis and, therefore, throw the latch out of the notch in arm 26 and into the notch 7 3 in arm 21. Preferably for these purposes the above described latch 25 is pivoted within the handle 15 at 60. The position of'the latch is controlled by means of a handle 61 on the shaft 62 on which is a forked member 63 which engages a pin 64 Said roller is mounted on a rod 66' which is normally pressed down; wardly against the top of the latch by spring 67' and is slidable in a block 68, pivoted at 168 directly above the pivot 60. lVith the parts in the position shown in Fig. 5, the latch is held firmly into engagement with the notch on arm 26.

After the latch is in this position and the aviator starts to move the handle back toward its vertical position as the airplane turns toward the target, he moves the handle 61 to shift the roller and spring-pressed arm to the left in Fig. 5. This exerts a stron downward pressure on the top of the latch to rotate it clockwise in Fig. 5, but this cannot occur because the under surface of the latch is in engagement with the arcuate portion 7 2 of the member 21. As soon, however, as the handle 15 becomes vertical, the latch snaps down into the notch 7 3 disconnecting handle 15 from the member 26 connecting it to the member 21. Subsequent tilting 0 the handle, therefore, will cause turning of the entire bomb sight around its vertical axis through the variable speed drive 16 to 20 as .explamed above.

In order to signal the turns to the pilot at the same time or otherwise cause turnlng of the craft, I have shown an arm 74 secured to the sleeve 22 and having at its lower end a pin 75 extending between two pivoted contacts 7677. When the pin 75 is in its central position, both contacts 7 677 are closed against a common contact 78 thereby causing both signal lamps 7980 to burn. When, however, the handle 15 is inclined to the right or left, the corresponding contact is opened extinguishing one of the lights and notifying the pilot that a turn should be made. As soon, however, as the straight ground track is arrived at, i. e., position F in Fig. 3, the handle 15 will occupy some position to one side or the other of the vertical which will cause the sight to rotate at a rate equal and opposite to the rate of turn of the airplane. At this time the handle should be brought to the vertical to light both lamps and the airplane flies a straight course to- Ward the target but with its longitudinal axis inclined at the drift angle.

In order to detect the time at which the aircraft reaches the straight line course toward the target, I may make use of the fact that at that time the sight is rotating at a rate equal and opposite to the turning of the airplane as above stated, which is merely another way of stating that the sight is rotationally standing still in space. Therefore, I may detect this point by also mounting on the platform 12 or otherwise coupling thereto a turn indicator gyroscope 120 having'a contact arm 121 connected to the precession axis 122 thereof which cooperates with the central or vertical live section 123- and dead sections 124125, the trolley being on 123 when the sight is not turning. When the trolley 121 is on the live section and switch 126 is closed, a signal may be given the observer such as by illuminating a small light 127 in the eye-piece only. The observer in operating this portion of the invention normally keeps switch 126 open but when he is approaching the target and nearing the straight line position he closes the switch 126 so-that as soon-as the turn indicator becomes vertical, i. e., as soon as the bombsight stands still in space, a signal will be given the observer that the straight line ground course has been reached, whereupon he at once will straighten up the handle 15 and signal the straight course to the pilot and stop the rotation of the bombsight on the era t. 1

reversing contacts 81-82 with a relatively stationary trolley 83 associated therewith. Said contacts control the servo motor 85 which turns the rudder 86 preferably through a directional gyroscope 87. Said gyroscope is preferably of the type shown in prior application No. 410,526 filed November 29, 1929, Elmer A. Sperry, Jr., inventor, and assigned to the assignee of the present invention, which type normally maintains its posi tion in space bu twhich can be caused to precess to the right or left by the application of torque about its horizontal axis, the turning of the gyroscope causing the turning of the plane with it. As shown, the contacts 8182 may be placed in circuit with solenoids 87'-88 mounted on the vertical ring of the gyroscope and adapted to exert opposite torques about the horizontal axis 89 thereof by electro-magnetic pull on the cores 90, 90 when one or the other of the solenoids is excited, the cores being fixed to the gyro casing 91. At the base of the gyroscope are reversing contacts 9293 and relative stationary trolley 94 in circuit with opposite windings 9596 which operate reversing clutches (not shown) on the wind driven servo motor 85. A follow-up connection in the form of flexible wires 97 may be provided from the servo motor to the pulley 98 on which trolley 94 is mounted. Preferably the solenoids 8788 are also controlled from the contacts 7 6'77 which operate the lights 7 980. This may be effected through a relay 99 so that when one light only is lit one of the relay magnets is deenergized and the relay closed on one side to excite one of the solenoids and vice versa, but when both lights are lit the magnets are equal in strength and the relays held open by the centralizing springs 100.

From the foregoing description, the operation of my invention as a piece of mechanism will be understood but in order to comprehend the use and advantages of my invention as a bomb sight and aligning as an objective mechanism reference will now be had to the diagrams of Figs. 3 and 4. Fig. 3

shows in plan how my invention operates in moved to the left.

As soon as the airplane is lined up with the target, as shown in position B, handle 15 will become vertical because the target is then dead ahead and the turning signal to the pilot will indicate a straight course. Under these conditions the control of the reflector 8 is automatically released in the vertical by the snapping over of latch 25 so that the sight is held trained on the target -by regulating the rate of turn of the entire sight instead of by tilting the reflector, the latter being maintained vertical by springs 23". Considering the position B as representing the beginning of the new setting, position C may represent the conditions one half second later when the rudder has responded to the turn signal now given by lamp 80 but before the airplane has turned. Now, if the airplane be turned to the left at a substantially constant rate, while the bomb sight is also turned to the left relative to space at a diminishing rate (to keep the line of sight S'T on the target), a series of positions may be plotted at say one half sec- 0nd intervals at C, D and E until there is established at F what may be termed directional equilibrium when the turning of the plane isarrested and the curving ground track shown in dottedelines. has become a straight line leading directly to the target.

scale 101 and pointer 102.

By my invention I am able to bring the plane quickly to position B to initiate or signal the turn of the rudder from B to G by the act of holding the sight on the target, and I am also able to secure and maintain ground synchronisin in advance of the straight portion of the ground track.

Referring now to Fig. 4, the target in position B has been brought to the center of the reticule by the rapid tilt of the reflecting member 8 about its lateral axis. The side tilt of 8 about a-b by the control handle 15, while engaged with quadrant 26, has maintained the target between the two retithe cule wires, while, at the same time, guiding the airplane to the head-on position by the coarse pilot director Simultaneous w1th the arrival at the head-on position, control handle 15 will be brought to the central position by the act of moving it as the airplane turns so as to keep the target between the reticule wires. In the central position, as the latch in the control handle 15 has been set to trip, quadrant 26 and, therefore, reflecting member 8 are left in the central 0- sition and quadrant 21 is now engaged with control handle 15. The coarse pilot director indicates zero or information to hold present iizading. The pilot lamps 79 and 80 are both A half second later position C is reached. The bomber has maintained the target on the cross wire 103 by adjusting hand wheels 44 at the top of control hand 15 and in so doing has changed the rate of tilt of the refleeting member about its lateral axis because of the follow-up connection 53 between the rate setting and tilting mechanism. The bomber must allow this small lapse of time to take place between B and C, Fig. 3, to make sure of the direction of drift as seen in C, Fig. 4. The bomberwill now tilt control handle 15 a small amount to the left as indicated by the target, for a left turn which will show up to the pilot by the left hand lamp remaining light. The pilot should interpret this signal to turn left at a predetermined rate, say three degrees per second. Assuming a value of wind that will bring the airplane to position D, Fig. 3, in one-half second when turning at the rate of three degrees per second, the target will appear on the reticule as in D, Fig. 4, which is the same as B but with this difference that the airplane is now turning to the left as the bomber determined at C that a left turn was required and the bomb sight has turned almost wholly with the airplane. In order to maintain the target between the reticule wires, the control handle 15 is pushed still further to the left, earing being such that this causes the bom sight to lag behind to the right as the airplane continues to turn left.

To make this point more clear, assume that the control handle 15 is not moved to the left further than enough to initiate the turn. The target and reticule relation will then shift to D which cannot be mistaken for the reverse 1*), Fig. 3, in order to maintain the target reticule relation E, Fig. 4, the right hand rotation will have to be increased until at position F, Fig. 3, this rate of rotation equals the rate of turn of the airplane in the opposite direction.

At position F, the control handle is again in its central position by the means of signal 127 as above explained. Both pilot lights 7 9-80 are then on, indicating that the heading is to be held and the correct drift angle is set up.

The alignment time may be shortened if I know approximately what my drift angle is and, therefore, I may approach position B at an angle with the approximate drift angle of the bomb sight cranked in by hand. I believe, however, that in most cases the bomber is not justified in guessing at his drift angle and, therefore, I prefer to approach the target at first head on.

A somewhat different form of the invention is illustrated diagrammatically in Fig. 7. In this figure only the parts that differ from Fig. 1 are shown and it will be understood that the other parts may remain substantially as shown in Fig. 1. According to this form of the invention the point at which the ground track becomes a straight line is determined automatically by the fact that this occurs only during the turn from position B to position F, and when the handle 15' becomes vertical. As above explained this point occurs when the bombsight is not rotating in azimuth with respect to space al' though it is rotating at an equal and opposite rate with respect to the airplane. I, therefore, provide a means so that the position of the bombsight is determined not with respect to the airplane but with respect to space or the ground. For this purpose I provide an auxiliary directional gyroscope 130 preferably mounted on the bombsi ht platform 12 as indicated by the dotte line enclosing the parts mounted on the latform as in Fig. 1. This gyroscope may e in all respects similar to the direction gyro 87 hereinbefore described and is likewise provided with torque solenoids 131-132 mounted on the vertical ring 133 and exerting opposite torques on the gyro 130 through the core 134 when excited. It will be understood that the gyro is mounted on the platform 12' for independent rotation about its vertical axis 135, the vertical ring having secured thereto a contact segment 136 cooperating with a trolley 137 on the platform. The gyro is also provided with a caging or locking device 138 adapted to lock the gyro when not in operation to centralize the same with its spinninhg axis 139. preferably in line with the si t.

In this instance, instead of having the handle 15' control the turning of the sight directly, said handle operates through the gyroscope. The gyroscope in turn governs the orientation of the sight, maintaining it in line with the target regardless of the tuming of the airplane. This last is accomplished by having the contacts 136 and 137 control the electro-magnets 138-139 which operate reversing clutches 140 and 141 normally idly driven in opposite directions by the motor 16 through the pinion 142 on the motor shaft meshing both with gear 143 of the clutch 141 and with a pinion 144 on the shaft 145 of the pinion 146, the latter meshing with the gear 147 of the clutch 140. When, therefore, the bombsight is lined up with the gyro,'trolley 137 stands on the dead section 136, but when the bombsight is turned to the right or left with respect to the gyro, the appropriate clutch is energized to return the bombsight into alignment with the gyroscope.

In order to bring the bombsight on the target the member 21 in this instance, actuated from the handle 15, operates a trolley or other contact 148 which rolls over the rheostat 149 having two windings, one of which 150 is in circuit with the solenoid 131 and the other 150 in circuit with the solenoid 132, so that the further the handle is tilted the greater the strength of the energized solenoid and the more rapid the precession of the gyroscope in azimuth. Current is led into the trolley 148 through a stationary arcuate segment 151 having a dead section 152 at its center. A brush 153 on member 21 slides over said arcuate segment. Current is, therefore, led into the trolley 148 unless the segment 21 and, therefore, the handle 15 are vertical, at which time the circuit is interrupted. This also interrupts the circuit through the solenoid 153 which normally withdraws the cage 138 so that at that time the cage 138 locks the gyroscope to the bombsight through the action of biasing spring 154.

The operation of this form of the invention is as follows: Up until the airplane and sight are brought into position B, that is, with the handle 15 vertical and the prism 8 locked in the horizontal position laterally, the operation is the same as in Fig. 1. At this point, however, the switch 126 .is closed so that the azimuth gyro assumes control of the orientation of thebombsight. The aviator moves the handle 15 as before to keep the sight on the target but in this case the motion of the bombsight is controlled entirely through the gyroscope 130, the gyroscope itself turning the sight oppositely to the turn of the aircraft and also keeping the sight on the target by being caused to slowly precess in azimuth through the application of torques about its horizontal axis through solenoids 131 or 132. The only function of the movements of the handle 15, therefore, is to correct for the diflerences in the rate of turn of the aircraft and the rate of turn of the sight which amounts to a lag of the sight behind the aircraft, which approaches zero in space as the straight ground track is approached. Or, stated diflerently, these two rates become equal and opposite at the instant the straight ground track is reached and, therefore, in this position the handle 15 becomes vertical at which time, due to the contact of finger 153 with dead section 152 the gyro control is rendered inoperative and the gyro locked centralized with respect to the bombsight. Therefore, from this point on the act of maintaining the bombsight onthe target steers the craft in a straight line toward the target either automatically through the gyro 87 as described in connection with Fig. 1 or by signals 79, 80 to the pilot as hereinbefore described. It will be understood that instead of locking gyro 130 at this time, this gyroscope might be used to steer the craft as explained in my prior Patent No. 1,880,671 dated October 4, 1932, for Bomb sights.

In accordance with the provisions of the patent statutes, I have herein described the principle and operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof, but I desire to have it understood that the apparatus shown is only illustrative and that the invention can be carried out by other means. Also, while it is designed to use the various features and elements in the combination and relations described. some of these may be altered and others omitted without interfering with the more general re sults outlined, and the invention extends to such use.

Having described my invention, what I claim and desire to secure by Letters Patent is:

1. In a bomb sight for aircraft, the combination with an optical system, variable speed means for rotating the same in azimuth, manually adjustable means for adjusting said first-named means to maintain the line of sight on the target, and means also operated by said manual means for causing turning of the craft until the ground track becomes a straight line.

2-. Ina bomb sight for aircraft, the combination with an optical system, variable speed means for rotating the same in azimuth, manually adjustable means for adjusting said first-named means to maintain the line of sight on the target, and means also operated by said manual means for causing turning of the craft until rotation of said optical system in space ceases.

3. In a bomb sight for aircraft, the combination with an optical system rotatable in azimuth, a common means for rotating said system to maintain the sight on the target and for simultaneously causing turning of the craft until the straight ground track is reached, and means for determining when such track is reached.

4. In combination with an aircraft, an

aligning mechanism on said craft, and automatic steering means controlled therefrom for aligning the ground track of the craft with the objective including a direction gyroscope for controlling the rudder both during the aligning operation and after the correct ground track has been reached.

5. In combination with an aircraft, an aligning mechanism on said craft, and automatic steering means controlled therefrom for aligning the ground track of the craft with the objective includin a direction gyroscope, and means governed by said aligning mechanism for causing through the gyroscope turning of the craft until the ground track becomes a straight line whereupon the gyroscope directs the craft in that line toward the objective.

6. In a bomb sight for aircraft, a target reflecting means, means for mounting the same for rotation in azimuth and for fore and aft tilting to follow the target, a control handle tiltable transversely for rotating said reflector in azimuth, and manual means also on said handle for tilting said reflector.

7. In a bomb sight for aircraft, a target re-' flecting means, means for mounting the same for rotation in azimuth and for fore anda ft tilting to follow the target, a variable speed drive for rotating said means, a variable speed drive for tilting said means, a control handle tiltable transversely for governing said first named variable speed drive, and manual means also on said handle for governing said second named means.

8. In a bomb sight for aircraft, a target sighting means, means for mounting the same for rotation in azimuth, for fore and aft tilting to follow the target and for lateral tilting to pick up the target, a control handle tiltable transversely, and shiftable means for causing said handle to tilt said means laterally or to rotate the same in azimuth.

9. In a bomb sight for aircraft, a target reflecting means, means for mounting the same for rotation in azimuth, for fore and aft tilting to follow the target and for lateral tilting to pick up the target and for causing said craft to line up with the target, means for locking said reflector laterally horizontally as it passes through horizontal, means for turning said reflector in azimuth to keep the target in sight and means actuated thereby for causing said craft to turn to align the ground track with the target.

10. In a bomb sight for aircraft, a target reflecting means, means for mounting the same for rotation in azimuth for fore and aft tilting to follow the target and for lateral tilting to pick up the target, a control handle tiltable laterally, a connection therefrom to tilt said reflector to pick up the target and for causing said craft to line up with the target, means for severing said connection as said handle passes through the vertical and for connecting said handle to turn said reflector in azimuth.

'11. The method of approaching a target with bombing aircraft having a bomb sight -8 rotatable in azimuth which comprises setting up a variable rate of turn of the sight sufficient to keep the sight on the target and causing, by such act, turning of the craft at a predetermined substantially constant rate.

12. The method 'of approaching a target with bombing aircraft having a bomb sight rotatable in.azimuth which comprises setting up a variable rate of turn of the sight sufiicient to keep the sight on the target, causing, by such act, turning'of the craft at a predetermined substantially constant rate and discontinuing the turn'when the rate of turn of the sight reaches zero in space.

13. In a bomb sight for aircraft, the combination with an optical system, variable speed means for rotating the same in azimuth, manually adjustable means for adjusting said first-named means to maintain the line of sight on the target, and automatic means also operated by said manual means for causing turning of the craft at a constant rate. until the ground track becomes a straight line.

1 4;,- In a bomb sight for aircraft, the com' bination with an optical system, variable speed-"means for rotating the same in azimuth,.m'anually adjustable means for adjusting said first-named means to maintain the line of sight on the target, means also operated by said manual means for causing turning of the craft, and means for causing said craft to fly on a straight ground track toward the target when absolute rotation of the sight ceases.

15. In a bomb sight for aircraft, the combination with a sight, means tiltable about a transverse axis to follow the target, of means for tilting said sight including a manually positionable means, a variable speed drive positioned therefrom for tilting said sight at a variable rate, and a direct connection from said means to said sight whereby a movement of said means to change the rate of tilt also immediately changes the tilt in the direction to bring the-target into the center of the field.

16. In a bomb sight for aircraft, the combination with a sight, means tiltable about a transverse axis to follow the target, of means for tilting said sightincluding a manually positionable means, a variable speed drive positioned therefrom for tilting said sight at a variable rate, and a direct connection from said means to said sight, the gear ratios be ing such that a given movement of the manual means imparts a greater direct tilting movement to the sight than a Variation in the variable speed drive but in the same di-' rection.

17. In a bomb sight for aircraft, the combination with an optical system, variable speed means for rotating the same in azimuth, manually adjustable means for adjusting said first-named means to maintain the line of sight on the target, means also operated by said manual means for causing turning of the craft, and means for determining the point at which the straight ground track is reached.

18. In a bomb sight for aircraft, the combination With an optical system, variable speed means for rotating the same in azimuth, manually adjustable means for adjusting said first-named means to maintain the line of sight on the target, automatic means also operated by said manual means for causing turning of the craft at a constant rate, and

=turn detecting means for detecting and signalling when the straight ground track is reached whereby the turning of both the craftand the sight on the craft may be stopped and the straight ground track followed to the target.

19. The method of approaching a target with bombing aircraft having a bomb sight rotatable in azimuth which comprises setting up a variab e rate of turn of the sight sulficient to keep the sight on the target, causing by such act, turning of the craft at a predetermined substantially constant rate, determining the point at which the turning of the craft and sight become equal and opposite, discontinuing both turning operations at that point, and proceeding on the straight ground track to the target.

20. In a bomb sight for aircraft, a sight directing means, means for mounting the same for orientation with respect to the craft, a directional gyroscope, means actuated therefrom for turning the sight oppositely to turning of the craft, and means for causing through said gyroscope turning of said sight to maintain it on the target.

21. In a bomb sight for aircraft, the combination with an optical system, variable speed means for rotating the same in azimuth, manually adjustable means for adjust ing said first-named means to maintain the line of sight on the target, and means also operated by said manual means for causing turning of the craft until" said manual means is positioned to stop rotation of said optical system.

22. In a bomb sight for aircraft, the combination with an optical system rotatable in azimuth, and a common means for rotating said system to maintain the sight on the target and for simultaneously causing turning of the craft until the straight ground track is reached.

23. In a bomb sight for aircraft, a sight directing means, means for mounting the same for orientation with respect to the craft, a directional gyroscope, means actuated therefrom for turning the sight oppositely to turning of the craft, and means actuated thereby for introducing the offset correction.

24. In a bomb sight for aircraft, a sight directing means, means for mounting the same for orientation with respect to the craft, a directional gyroscope, means actuated therefrom for turning thesight oppositely to turning of the craft through the drift angle, and means for throwing out said gyro-controlled means when the absolute rate of rotation of the sight reaches'zero.

25. In a bomb sight for aircraft, a sight directing means, means for mounting the same for orientation with respect to the craft, a directional gyroscope, means actuated therefrom for turning the sight, and means for maintaining the sight on the target including torque-applying means controllable at will for exerting torques about the horizontal axis of said gyroscope.

26. In a bomb sight for aircraft a sight directing means, means for mounting the same for orientation with respect to the craft, a directional gyroscope, means actuated therefrom for turning the sight, means for maintaining the sight on the target including torque-applying means controllable at will for exerting torques about the horizontal axis of said gyroscope, and means for rendering said torque means inoperative when the straight ground track is reached.

27. In combination with an aircraft, an objective aligning mechanism on said craft, means for steering the craft on a fixed heading, means whereby said mechanism in keep ing the craft headed toward the objective modifies said steering means until a straight ground track toward the objective is reached, and means for causing said steering means to maintain a straight ground course toward the objective when said straight ground track is reached.

28. In combination with an aircraft, an objective aligning mechanism on said craft, a servo motor for steering the craft, means for controlling said servo motor from said mechanism, a directional gyroscope for also controlling saidservo motor, and means for transferring the-control of said servo motor from said mechanism to said directional gyroscope when a straight ground track is reached.

29. In combination with a dirigible aircraft, an aligning mechanism on said craft for aligning the craft with its objective, directional means on the craft for maintaining a predetermined heading, and means whereby said mechanism introduces a drift correction in said heading by the act of maintaining said mechanism aligned with said objective.

30. In combination with a dirigible aircraft, an aligning mechanism on said craft for aligning the craft with its objective, directional means on the craft for maintaining a predetermined heading, means whereby said mechanism introduces a drift correction in said heading by the act of maintaining said mechanism align d with said objective, and means adapted to be rendered effective when said craft is on the drift corrected course for steerin from said directional means.

31. n a means for directing an automatically steered aircraft toward its objective by a straight course, means rotatably mounted on the craft and adapted to be maintained in line with the objective, directional means on the craft adapted to maintain a fixed position in azimuth. and automatic means for steering the craft from both of said other means whereby the craftzis headed at such an angle to said aligning means that the ground course becomes a straight line toward the target.

32. In a means for directing an automatically steered aircraft toward its objective by a straight course, means rotatably mounted on the craft and adapted to be maintained in line with the objective, directional means on the craft adapted to maintain a fixedposition in azimuth, and means actuated by the turning of said first-named means with respect to the craft for causing turning of the craft until said means stops turning with respect to said directional means when the straight ground track is reached.

33. In apilot director adapted for bombing planes having a bombsight, a free gyroscope adapted to maintain a straight course, torque-applying means for exerting torques on said gyroscope about a horizontal axis to cause slow precession thereof in azimuth and consequent turning of the plane, and means on the bombsight for controlling said torque means as the bombsight is moved.

' MORTIMER F. BATES. 

